2 <!DOCTYPE modulesynopsis SYSTEM "../style/modulesynopsis.dtd">
3 <?xml-stylesheet type="text/xsl" href="../style/manual.en.xsl"?>
4 <!-- $LastChangedRevision$ -->
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23 <modulesynopsis metafile="mod_substitute.xml.meta">
25 <name>mod_substitute</name>
26 <description>Perform search and replace operations on response bodies</description>
27 <status>Extension</status>
28 <sourcefile>mod_substitute.c</sourcefile>
29 <identifier>substitute_module</identifier>
32 <p><module>mod_substitute</module> provides a mechanism to perform
33 both regular expression and fixed string substitutions on
38 <name>Substitute</name>
39 <description>Pattern to filter the response content</description>
40 <syntax>Substitute <var>s/pattern/substitution/[infq]</var></syntax>
41 <contextlist><context>directory</context>
42 <context>.htaccess</context></contextlist>
43 <override>FileInfo</override>
46 <p>The <directive>Substitute</directive> directive specifies a
47 search and replace pattern to apply to the response body.</p>
49 <p>The meaning of the pattern can be modified by using any
50 combination of these flags:</p>
53 <dt><code>i</code></dt>
54 <dd>Perform a case-insensitive match.</dd>
55 <dt><code>n</code></dt>
56 <dd>By default the pattern is treated as a regular expression.
57 Using the <code>n</code> flag forces the pattern to be treated
58 as a fixed string.</dd>
59 <dt><code>f</code></dt>
60 <dd>The <code>f</code> flag causes mod_substitute to flatten the
61 result of a substitution allowing for later substitutions to
62 take place on the boundary of this one. This is the default.</dd>
63 <dt><code>q</code></dt>
64 <dd>The <code>q</code> flag causes mod_substitute to not
65 flatten the buckets after each substitution. This can
66 result in much faster response and a decrease in memory
67 utilization, but should only be used if there is no possibility
68 that the result of one substitution will ever match a pattern
69 or regex of a subsequent one.</dd>
72 <example><title>Example</title>
73 <highlight language="config">
75 AddOutputFilterByType SUBSTITUTE text/html
76 Substitute s/foo/bar/ni
81 <p>If either the pattern or the substitution contain a slash
82 character then an alternative delimiter should be used:</p>
84 <example><title>Example of using an alternate delimiter</title>
85 <highlight language="config">
87 AddOutputFilterByType SUBSTITUTE text/html
88 Substitute "s|<BR */?>|<br />|i"
93 <p>Backreferences can be used in the comparison and in the substitution,
94 when regular expressions are used, as illustrated in the following example: </p>
95 <example><title>Example of using backreferences and captures</title>
96 <highlight language="config">
98 AddOutputFilterByType SUBSTITUTE text/html
99 # "foo=k,bar=k" -> "foo/bar=k"
100 Substitute "s|foo=(\w+),bar=\1|foo/bar=$1"
105 <p>A common use scenario for <code>mod_substitute</code> is the
106 situation in which a front-end server proxies requests to a back-end
107 server which returns HTML with hard-coded embedded URLs that refer
108 to the back-end server. These URLs don't work for the end-user,
109 since the back-end server is unreachable.</p>
111 <p>In this case, <code>mod_substutite</code> can be used to rewrite
112 those URLs into something that will work from the front end:</p>
114 <example><title>Rewriting URLs embedded in proxied content</title>
115 <highlight language="config">
116 ProxyPass /blog/ http://internal.blog.example.com
117 ProxyPassReverse /blog/ http://internal.blog.example.com/
119 Substitute "s|http://internal.blog.example.com/|http://www.example.com/blog/|i"
123 <p><directive module="mod_proxy">ProxyPassReverse</directive>
124 modifies any <code>Location</code> (redirect) headers that are sent
125 by the back-end server, and, in this example,
126 <code>Substitute</code> takes care of the rest of the problem by
127 fixing up the HTML response as well.</p>